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run code in 150+ php & hhvm versions
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<?php $a = array(); $a[] = array('1',null); $a[] = array('1','2'); $a[] = array('2',null); $a[] = array('2','2'); $a[] = array('1',null); $a[] = array('2','2'); print_r(array_map("unserialize", array_unique(array_map("serialize", $a))));
Output for 4.3.0 - 5.6.28, hhvm-3.10.0 - 3.12.0, 7.0.0 - 7.1.0
Array ( [0] => Array ( [0] => 1 [1] => ) [1] => Array ( [0] => 1 [1] => 2 ) [2] => Array ( [0] => 2 [1] => ) [3] => Array ( [0] => 2 [1] => 2 ) )